1. Field of the Invention
The present invention relates generally to a method and apparatus for the management and control of various flow streams related to the operation of a fuel cell. The present invention relates more specifically to a fuel cell gas management system which includes subsystems for conditioning the temperature and humidity of the air or other oxidant supplied to a fuel cell's cathode, for anode fuel humidity retention, and for cooling water circulation.
2. Description of Related Art
Fuel cells generate electrical energy by chemical reaction without altering the electrodes or electrolyte of the cell itself The utility of fuel cells has been known since at least as early as 1939, when Grove demonstrated that electrolysis of water could be reversed using platinum electrodes. Further developments in the fuel cell field have included the development of proton exchange membrane (PEM) fuel cells, phosphoric acid fuel cells, alkaline fuel cells, and fuel cells incorporating reformer technology to crack hydrocarbons such as gasoline to obtain hydrogen to feed the fuel cell.
Fuel cells have found application in a number of fields. One area of particular interest has been the application of fuel cell technology in electrically-powered automobiles. In automotive applications, weight and space are at a premium, and therefore, the fuel cell and its supporting systems must be as small and lightweight as possible. Moreover, because automotive applications subject equipment to a wide and rapidly fluctuating range of operating conditions such as temperature, humidity, etc., equipment utilized in such applications must be capable of withstanding and operating under a variety of conditions. Equipment utilized in automotive applications must also be sufficiently rugged to withstand the vibrations and stresses induced by over-the-road use.
Fuel cells generally require two independent gas flow circuits for delivering reactant gases to the anode and the cathode of the fuel cell. In PEM fuel cells, these gas flow circuits comprise an anode circuit for feeding the fuel, generally hydrogen, to the fuel cell; and a cathode circuit for feeding the oxidant, typically air from the ambient, to the fuel cell. In order to maintain proper operating conditions for the fuel cell, the temperatures and humidities of the anode and cathode circuits must be precisely controlled to avoid drying out the electrolyte or otherwise damaging the fuel cell, and thereby stopping the flow of electricity from the fuel cell.
Several systems for conditioning the gas flow circuits of a fuel cell have been proposed. For example, U.S. Pat. No. 3,516,867 to Dankese discloses a fuel cell system including a dehumidifier and a humidifier for conditioning the fuel cell's gas streams. The humidification portion of this system achieves moisture transfer through a partition. This type of humidification system has been found inefficient for automotive applications, mainly because of the large surface areas required to transfer the necessary quantity of moisture to the gas streams, and because of the undesirable weight of such large-scale systems. In addition, large quantities of heat energy are consumed in vaporizing moisture in this type of humidification system, which energy consumption reduces system efficiency.
U.S. Pat. No. 3,669,751 to Richman discloses a fuel cell, hydrogen generator, and heat exchanger system, wherein the reactant air to be supplied to the fuel cell is brought into evaporative contact with the wet electrolyte to humidify the reactant air. The system of Richman suffers similar disadvantages to that of Dankese; namely, the requirement of large surface areas for effecting moisture transfer and the resulting weight of system components, as well as the consumption of considerable energy in vaporizing the moisture.
In addition to cathode humidification, existing fuel cell technology requires the humidification of the hydrogen fuel stream input to the fuel cell's anode, in order to prevent drying out the electrolyte within the fuel cell. This requirement of anode humidification adds additional components to the fuel cell's gas management system, resulting in undesirable increased weight and expense. Moreover, known humidification systems such as membrane humidifiers or systems utilizing airflow through beds of wetted spheres consume considerable energy in vaporizing water to provide the required humidification. Therefore, it has been found that known methods of anode humidification are unsuited to automotive applications.
Thus it can be seen that a need yet exists for a lightweight, efficient means of conditioning the oxidant flow to the cathode inlet of a fuel cell.
A need further exists for a method and apparatus for conditioning the anode inlet to a fuel cell, which minimizes the weight and expense of associated components.
It is to the provision of a method and apparatus of fuel cell gas management meeting these and other needs that the present invention is primarily directed.